Introducing a standard method for experimental determination of the solvent response in laser pump, x-ray probe time-resolved wide-angle x-ray scattering experiments on systems in solution

WOS:000323520600021International audienceIn time-resolved laser pump, X-ray probe wide-angle X-ray scattering experiments on systems in solution the structural response of the system is accompanied by a solvent response. The solvent response is caused by reorganization of the bulk solvent following the laser pump event, and in order to extract the structural information of the solute, the solvent response has to be treated. Methodologies capable of doing so include both theoretical modelling and experimental determination of the solvent response. In the work presented here, we have investigated how to obtain a reproducible solvent response-the solvent term-experimentally when applying laser pump, X-ray probe time-resolved wide-angle X-ray scattering. The solvent term describes difference scattering arising from the structural response of the solvent to changes in the hydrodynamic parameters: pressure, temperature and density. We present results based on NIR and dye mediated solvent heating, and demonstrate that the solvent response is independent of the heating method. The NIR heating is shown to be rendered unusable by higher order effects under certain experimental conditions, while the dye mediated solvent heating is demonstrated to exhibit first order behaviour with respect to the amount of energy deposited in the solution. We introduce a standardized method for recording solvent responses in laser pump, X-ray probe time-resolved X-ray wide-angle scattering experiments by using dye mediated solvent heating. Furthermore, we have generated a library of solvent terms, which can be used to describe the solvent term in any TRWAXS experiment, and made it available online

Initial heating mechanism of fluids after photoexcitation of molecules in various phases

Heating rates after photoexcitation of several organic molecules have been studied by the transient grating spectroscopy with sub-picosecond laser pulses in solution and supercritical fluids. The rise time of the acoustic signal produced by the energy dissipation process of the hot ground state molecule was monitored. The acoustic signal was analyzed by an equation including the acoustic damping. The solvent temperature rise times in various media have been determined. The temperature rise times in solutions were longer than the vibrational energy relaxation times of the solutes determined by the transient absorption measurements. The difference was discussed in terms of the contribution of vibrational states in the energy transfer pathways from the solute to the solvent. It was found that the hydrogen-bonding between the solute and solvent play important roles in determining the energy transfer pathway from the solute to the solvent

Contributions of transient absorption and population lens in thermal lens spectroscopy

Contaminations of the population lens and transient absorption in the observed thermal lens signal sometimes cause a misinterpretation of the signal. Recently, we have developed several methods to evaluate the relative contributions of these components in the observed thermal lens signal. These methods with recent results are summarized, and merits and limitations of each method are discussed